They think we make up doctrine like they do
They don't have a clue as to how doctrine comes about. They figure whatever Rome spouts is doctrine, founded on church fathers and declarations from the magisterium and pontifical posturings.
They haven't a clue as to the difference between the doctrines of God's word and the doctrines of men since they believe some men are God and therefore have a right to create doctrine out of men's opinions.
Doctrine is Scriptural teaching, based on God's word alone. If it isn't in the Bible, it is not to be utilized as the basis for our faith or practice.